The present invention relates to a system for reproducing digital signals at a manually controllable frequency which may differ from the frequency at which the digital signals have been derived from original analog signal.
Editing a plurality of recorded signals into a combined signal for transcribing to a single output tape requires precision speed control for adjusting the speed of one tape with respect to another to permit the operator to locate an exact point of transition from one material to another so that they can be interconnected without appreciable discontinuities between them.
Conventionally, the original analog signal is sample and converted into a digital signal and stored as a pulse-code modulated data in a memory. The stored data is read out of the memory at a manually controllable frequency to permit the operator to locate the correct point of connection. Since the original sampling frequency is at least twice the bandwidth of the analog signal as is well known in the art, the bandwidth of the reproduced signal may exceed the upper frequency limit of a bandwidth to which the sampling frequency of the read out data should correspond if the speed of reproduction is lower than the speed at which the original signal is recorded into the memory. The frequency components above such upper limit cause a foldover distortion in the reproduced signal.
Another problem associated with the variable speed reproduction of sampled data resides in the fact that analog low-pass filters would be required in the amount corresponding to different reproduction speeds for smoothing out the reproduced digital signal.